This invention relates generally to sensing systems that employ a nanopore sensor, and more particularly relates to techniques for sensing species as the species translocate through a nanopore sensor.
Solid state and biological nanopores are increasingly the focus of considerable effort towards the development of a low cost, high throughput sensing system that can be employed for sensing a wide range of species, including single molecules. For example, there is has been proposed the use of solid state nanopores for enabling single-molecule DNA sequencing technology. While single DNA bases produced by enzymatic cleavage of DNA have been detected and differentiated using modified protein nanopores, the goal of sequencing a single-stranded DNA (ssDNA) molecule by translocation of the molecule through a nanopore has not yet been fully realized.
One proposed approach for nanopore sensing is based on a method in which there is detected a modulation of ionic current passing through a nanopore that is disposed in a membrane or other support structure. Given a molecule that is provided in an ionic solution to be translocated through a nanopore, as the molecule translocates through the nanopore, the ionic current that passes through the nanopore is correspondingly decreased from the ionic current passing through the nanopore without a molecule. This nanopore sensing approach is limited in that it is in general quite difficult to record the small picoampere ionic current signals that are characteristic of molecular nanopore translocation at a bandwidth that is consistent with very fast molecular translocation speeds. The speed of a DNA molecule translocation through a nanopore can be ˜1 μs/nucleotide. Furthermore, the recording of such small current signals at high bandwidth in a parallel multiplexed format has been shown to be extremely difficult.
To circumvent the technical challenges of the ionic current measurement method for nanopore sensing, several alternative nanopore sensing methods have been proposed. Such alternative methods can be generalized as directed to an effort to record larger and relatively more-local nanopore signals employing electronic sensors that are integrated with the nanopore. These nanopore sensing methods include, e.g., measurement of capacitive coupling across a nanopore and tunnelling current measurements through a species translocating a nanopore. While providing interesting alternative sensing techniques, such capacitive coupling and tunnelling current measurement techniques have not yet improved upon the conventional ionic current detection technique for nanopore sensing, and ionic current detection techniques remain challenged by signal amplitude and signal bandwidth issues.